Molecular Physics — UPSC IFoS 2019 Physics PYQ

The first rotational line of {}^{12}\text{C}^{16}\text{O} is observed at 3\cdot 84235~\text{cm}^{-1} and that of {}^{13}\text{C}^{16}\text{O} at 3\cdot 67337~\text{cm}^{-1}. Assuming the mass of {}^{16}\text{O} to be 15\cdot 9949~\text{u}, calculate that of {}^{13}\text{C}.